The present invention relates to a light conducting plate for a back lighting device of an edge-light type to be used in a display device such as a liquid crystal display, and to a back lighting device provided with a linear light source and others.
As back lighting devices for a liquid crystal display device such as a liquid crystal Television or a portable personal computer, those of a so-called edge-light type in which the light emitted from a linear light source irradiates the liquid crystal display device through a light conducting plate are often used. The back lighting device is constructed by disposing a linear light source opposite to a light-inlet end face of the light conducting plate. The light conducting plate is made of an acrylic resin, and has an about wedge-like shape in which a reflecting face for reflecting the introduced light into the light conducting plate and a light-outlet face for allowing the light to emit to the outside of the light conducting plate are formed in a non-parallel configuration.
A diffusing plate, a first prism sheet, a second prism sheet, and a protective sheet are superposed on the light-outlet face of the light conducting plate, and a reflecting plate is superposed on the reflecting face of the light conducting plate. The light source which is housed in a chassis is facing the light-inlet end face on a thick side of the light conducting plate. The first and second prism sheets each have a prism surface on an upper surface or a lower surface thereof. The reflecting face of the light conducting plate is subjected to a white dot printing process or a surface-roughening process to aid the reflection and scattering of the introduced light for improvement in the luminance of the light-outlet face. In recent years, due to the demand in cost reduction and the problems of exhaust liquid of the printing ink, the reflecting face is often subjected to the surface-roughening process rather than the printing process.
In a back lighting device having such a construction, the light emitted from the linear light source is introduced through the light-inlet end face of the light conducting plate to be reflected by the reflecting face and the reflecting plate and is transmitted through the light conducting plate in a direction intersecting the light-inlet end face to emit through the light-outlet face of the light conducting plate. The light that has emitted repeats a process of being diffused and condensed while being transmitted through the diffusing plate and the two prism sheets, thereby to irradiate the liquid crystal display device disposed on an upper layer of the back lighting device.
Also, in recent years, due to the demand for thickness reduction and cost reduction of the liquid crystal display devices, those without the use of a diffusing plate or those with the use of only one prism sheet are being developed. The luminance of such a back lighting device is heightened by performing a prism processing on the light-outlet (light-emitting) face of the light conducting plate, or by devising a prismatic shape of the prism sheet.
As described above, a light-scattering surface is formed on the reflecting face of the light conducting plate for a back lighting device by performing a white dot printing process or a satin finishing process on the entire region of the reflecting face. This allows the introduced light to be scattered by the reflecting face to reduce the luminance nonuniformity of the light-outlet face. Further, in some light conducting plates, the density of dots or the density of recesses and projections on the light-scattering surface is made different between a region near to the light source and a region distant from the light source. For example, by allowing the density on the near region to be lower than that on the distant region, high emission of light caused by being the inlet side of the introduced light is buffered. This reduces the difference in the luminance of the light-outlet face between the side near to the light source and the side distant from the light source.
However, since the region of the light-outlet face near to the light-inlet end face is influenced by refraction which occurs when the light emitted from the light source is transmitted through the light-inlet end face, there will be a large difference in luminance on the region as compared with a central region of the light-outlet face, raising a problem that abnormal light-emission occurs even if the density of dots or the density of recessed and projections on the reflecting face is reduced. Further, there has been a problem that, although a reflecting tape is allowed to adhere to the surface opposite to the light-inlet end face for preventing leakage of the light introduced into the light conducting plate, abnormal light-emission occurs also on a region of the light-outlet face near to the reflecting tape by being influenced from reflection at the reflecting tape.
Furthermore, in the back lighting device having the aforementioned construction, the reflecting face of the light conducting plate is often subjected to a surface-roughening process rather than a printing process, as described before. In the case where a light conducting plate subjected to the printing process is used, the prism sheet is disposed so that the prism surface thereof faces upwards. However, in the case where a light conducting plate subjected to the surface-roughening process is used, conversely, the prism sheet is disposed so that the prism surface thereof faces towards the light conducting plate side. Since the light-inlet end face of the light conducting plate is a mirror-like surface, the light-inlet end face is imaged when the prism surface of the prism sheet faces towards the light conducting plate, thereby raising a problem that a dark line appears on the light-outlet face.
The present invention has been made in order to solve the aforementioned problems, and an object of the present invention is to provide a light conducting plate for a back lighting device and a back lighting device in which the abnormal light emission of the light-outlet face is prevented by disposing a light-scattering region and a remainder region on the reflecting face. Another object of the present invention is to provide a light conducting plate for a back lighting device and a back lighting device in which the dark line on the light-outlet face is removed by performing a surface-roughening process on the light-inlet end face. Still another object of the present invention is to provide a light conducting plate for a back lighting device and a back lighting device in which the leakage of light caused by the surface roughening process of the light-inlet end face is prevented.
A light conducting plate for a back lighting device according to the present invention comprises a light-inlet end face for introducing light emitted from a light source to be disposed facing said light conducting plate; a reflecting face for reflecting the light introduced through said light-inlet end face; and a light-outlet face disposed opposite to said reflecting face for allowing the light reflected from the reflecting face to emit therethrough, characterized in that said reflecting face includes a light-scattering region and a remainder region, and the remainder region is located on a side near to said light-inlet end face.
In this invention, the light-scattering region is not formed on a region of the reflecting face near to the light-inlet end face. The light-scattering region means a region where a face scattering light is formed, and the remainder region means a region where the light-scattering region is not formed. The remainder region has a smaller degree of light scattering as compared with the light-scattering region and, therefore, the scattering of the introduced light is reduced on the remainder region, whereby a side of the light-outlet face closer to the light-inlet end face shows the same degree of luminance as the central portion by suppression of the abnormal light-emission.
A light conducting plate for a back lighting device according to the present invention comprises a light-inlet end face for introducing light emitted from a light source to be disposed facing said light conducting plate; a reflecting face for reflecting the light introduced through said light-inlet end face; and a light-outlet face disposed opposite to said reflecting face for allowing the light reflected from the reflecting face to emit therethrough, characterized in that said reflecting face includes a light-scattering region and the remainder region, and the remainder region is located on a side near to an opposite face from said light-inlet end face.
In this invention, the light-scattering region is not formed on a region of the reflecting face near to an opposite face from the light-inlet end face. The remainder region except the light-scattering region on the reflecting face has a smaller degree of light scattering as compared with the light-scattering region and, therefore, the scattering of the introduced light is reduced on the remainder region, whereby a side of the light-outlet face distant from the light-inlet end face shows the same degree of luminance as the central portion by suppression of the abnormal light-emission.
A light conducting plate for a back lighting device according to the present invention is characterized in that said reflecting face includes a remainder region except said light-scattering region, on the side near to said light-inlet end face and on the side near to an opposite face from said light-inlet end face.
In this invention, the light-scattering region is not formed on regions of the reflecting face near to and distant from the light-inlet end face. The remainder region has a smaller degree of light scattering as compared with the light-scattering region. The scattering of light is reduced on the inlet side and its opposite side of the light conducting plate where more light is reflected in a complex manner, whereby the region near to and the region distant from the light-inlet end face both show the same degree of luminance as the central portion to produce uniform luminance of the light-outlet face.
A light conducting plate for a back lighting device according to the present invention is characterized in that said remainder region is a region having less irregularity of reflection of the introduced light than said light-scattering region.
Further, a light conducting plate for a back lighting device according to the present invention is characterized in that said light-scattering region has been subjected to dot printing on a surface thereof, and said remainder region is a mirror-like surface.
Still further, a light conducting plate for a back lighting device according to the present invention is characterized in that said light-scattering region has an irregular surface, and said remainder region is a mirror surface.
In this invention, said light-scattering region is formed, for example, by performing a dot ink printing process with white ink. The remainder region that maintains a mirror state at the time of molding without printing has a less degree of irregular reflection of light than the light-scattering region and has reduced concentration of light, so that the luminance of the light-outlet face becomes uniform.
A back lighting device according to the present invention comprises a light conducting plate described above; a light source disposed facing said light-inlet end face of said light conducting plate; and a reflector being superposed on said reflecting face of said light conducting plate, characterized in that said reflector includes a light-absorbing region located on a region facing said remainder region of said light conducting plate.
In this invention, since the light-absorbing region is formed on the region of the reflector located facing the remainder region of the light conducting plate, the reflected light on a side of the reflector near to and/or distant from the light source is absorbed, whereby the abnormal light-emission is further suppressed.
Furthermore, a light conducting plate for a back lighting device according to the present invention comprises a light-inlet end face for introducing light emitted from a light source to be disposed facing said light conducting plate; a reflecting face having a light-scattering region for reflecting the light introduced through said light-inlet end face; and a light-outlet face disposed opposite to said reflecting face for allowing the light reflected from the reflecting face to emit therethrough, characterized in that said light-inlet end face is a roughened surface.
In this invention, since the light-inlet end face is a roughened surface, the light emitted from the light source is scattered by the light-inlet end face to be introduced into the light conducting plate, thereby preventing generation of a dark line on the light-outlet face.
A light conducting plate for a back lighting device according to the present invention is characterized in that said light-inlet end face is a roughened surface, and said reflecting face includes the remainder region except said light-scattering region, on the side near to said light-inlet end face.
In this invention, the region of the reflecting face near to the light-inlet end face maintains, for example, a mirror state without forming a light-scattering region. As described above, the imaging of the light-inlet end face in the case where the remainder region is formed by surface roughening instead of printing is prevented by roughening the light-inlet end face. However, when the degree of roughness of the light-inlet end face is too large, leakage of light occurs. By allowing the region of the reflecting face near to the light-inlet end face to be maintained in a mirror-like surface state, the region has a smaller light scattering as compared with the light-scattering region. Since reflection and scattering of the light introduced into the light conducting plate is suppressed in the remainder region, leakage of light caused by the surface roughening of the light-inlet end face is prevented.
A light conducting plate for a back lighting device according to the present invention is characterized in that said remainder region is disposed in a central region along said light-inlet end face.
In this invention, since the regions of the light-outlet face corresponding to both end sides of the light-inlet end face have a low luminance than the central region, it is sufficient that the region for suppressing leakage of light is formed only on the central portion where the luminance tends to be high, so that the light-scattering region is located on both end sides. This can prevent leakage of light on the light-outlet face, and too low luminance of the region corresponding to both ends of the light source can be avoided.
A light conducting plate for a back lighting device according to the present invention is characterized in that said light-scattering region has an irregular surface, and said remainder region is a mirror-like surface.
In this invention, the light-scattering region has a face where the reflecting face is made to include recesses and projections, and the method for forming them is, for example, chemical etching, sand blasting, molding of the light conducting plate with a mold pattern, or a dot pattern formation by laser radiation. The remainder region maintains the mirror-like surface formed at the time of injection molding of the light conducting plate. By not performing the printing process on the reflecting face, the cost can be reduced, and the problem of exhaust liquid of the printing ink can be solved.
A back lighting device according to the present invention is characterized by comprising a light conducting plate described above; and a light source disposed facing said light-inlet end face of said light conducting plate.
In this invention, the back lighting device is constructed by disposing the light source facing the light-inlet end face of the light conducting plate, whereby the luminance of the light-outlet face is made uniform as described above.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.